1. Field of the Invention
This invention relates to solid-state light emitting devices and signage with photoluminescence wavelength conversion and more particularly photoluminescent compositions therefor. In particular, although not exclusively, the invention concerns devices and signage based on LEDs (Light Emitting Diodes). The invention further concerns a method of manufacturing photoluminescence wavelength conversion components for solid-state light emitting devices and photoluminescence signage surfaces for light emitting signage.
2. Description of the Related Art
White light emitting LEDs (“white LEDs”) are known and are a relatively recent innovation. It was not until LEDs emitting in the blue/ultraviolet part of the electromagnetic spectrum were developed that it became practical to develop white light sources based on LEDs. As taught, for example in U.S. Pat. No. 5,998,925, white LEDs include one or more phosphor materials, that is photoluminescent materials, which absorb a portion of the radiation emitted by the LED and re-emit light of a different color (wavelength). Typically, the LED chip or die generates blue light and the phosphor(s) absorbs a percentage of the blue light and re-emits yellow light or a combination of green and red light, green and yellow light, green and orange or yellow and red light. The portion of the blue light generated by the LED that is not absorbed by the phosphor material combined with the light emitted by the phosphor provides light which appears to the eye as being nearly white in color.
Due to their long operating life expectancy (>50,000 hours) and high luminous efficacy (70 lumens per watt and higher) high brightness white LEDs are increasingly being used to replace conventional fluorescent, compact fluorescent and incandescent light sources.
Typically the phosphor material is mixed with a silicone or epoxy material and the mixture applied to the light emitting surface of the LED die. As disclosed in United States patent application US 2008/0218992 A1 to Li, it is also known to provide the phosphor material as a layer on, or incorporate the phosphor material within an, optical component that is located remotely to the LED die.
United States patent application US 2007/0240346 A1, to Li et al., teach a solid-state light emitting sign in which blue light from an LED is used to excite phosphor materials on a light emitting signage surface to generate a desired color of light.
It is an object of the present invention to provide a photoluminescent composition for solid-state light emitting devices and signage with photoluminescence wavelength conversion that in part at least overcomes the limitations of the known devices.